JCV is a human polyoma virus which virus which has been isolated from the brain of patients with chronic demyelinating disease, progressive multifocal leukoencephalopathy (PML). This oncogenic virus is associated with the development of brain tumors including glioblastomas, medulloblastomas, neuroblastomas and other tumor of neural origin. JCV exhibits a highly specific host range and tissue specificity. In vitro, JCV grows exclusively in primary human fetal glial cells. Several studies have shown that the restricted host range of JCV to brain tissue in cell culture is determined at the transcriptional level. However, the mechanisms that govern tissue-specific transcription of this virus in brain cells remain unknown. The aim of the research outlined in this proposal is to define the mechanisms by which the JC virus genome is regulated transcriptionally in a tissue-specific manner. The experimental design includes: (1) identification of the cis-acting transcriptional control elements of the viral genome; (2) characterization and purification of the trans-acting regulatory proteins from permissive cells and tissue that by interacting with the cis-acting sequences that control transcription of the viral genome; (3) cloning of the gene encoding the regulatory proteins, and large- scale production of these proteins for detailed structural/functional studies. The information gained from these manipulations and analyses should increase understanding of the mechanisms that modulate transcription of the viral genes in neural cells and the tumorgenicity of this virus in brain.